1. Field of the Invention
The present invention relates to a pressure transducer for sensing the pressure of a gas or liquid for conversion of the pressure value to an electrical signal and then outputting the signal.
2. Description of the Related Art
U.S. Pat. No. 4602513 discloses a pressure transducer which has a housing provided in its head with a diaphragm displaceable by an external pressure; a magnetoresistive element, whose electric resistance is varied in response to changes in the magnetic field, fixed to the bottom of the housing; and a permanent magnet disposed opposite the magnetoresistive element and displaceable as the diaphragm is displaced.
This transducer is capable of measuring the external pressure by electrically detecting variations in the electric resistance of the magnetoresistive element. When the transducer is assembled, it is necessary to adjust the magnetic field strength which acts on the magnetoresistive element (magnetic sensitivity adjustment) and to adjust the positional relationship in the direction in which the magnet and element are displaced (O-point adjustment).
Then, this transducer is so designed that two holders for respectively holding the permanent magnet and the magnetoresistive element are adapted to be pressed and to yield at their ends by the action of adjustable screws provided for making the two adjustments.
With this adjustment method, one of the two adjustments, such as the magnetic sensitivity or O-point, is out when the other is made so that an adjusting operation involves repetition of the two adjustments and thus involves difficulty, requiring much time.
Besides, if the holders are caused to yield by such adjustments, the magnetoresistive element is caused to incline and the distance between the magnetoresistive element and the permanent magnet is varied when the magnet is displaced in detecting pressure. This will mean the failure to obtain a precise measurement.
Moreover, a characteristic of the magnetoresistive element is changed in accordance with changes in temperature. In addition, it has the property of a non-linear change with respect to temperature. Thus, difficulty is involved in compensating (temperature compensation) for the value detected in accordance with the temperature. The disadvantage derived from such a transducer is that a considerable number of errors are made in the measurements carried out in an environment where the temperature changes.